向字符串类添加扩展方法 - C#
不确定我在这里做错了什么。扩展方法无法识别。
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Text.RegularExpressions;
using StringExtensions;
namespace ConsoleApplication1
{
class Program
{
static void Main(string[] args)
{
RunTests();
}
static void RunTests()
{
try
{
///SafeFormat
SafeFormat("Hi There");
SafeFormat("test {0}", "value");
SafeFormat("test missing second value {0} - {1}", "test1");
SafeFormat("{0}");
//regular format
RegularFormat("Hi There");
RegularFormat("test {0}", "value");
RegularFormat("test missing second value {0} - {1}", "test1");
RegularFormat("{0}");
///Fails to recognize the extension method here
string.SafeFormat("Hello");
}
catch (Exception ex)
{
Console.WriteLine(ex.ToString());
}
Console.ReadLine();
}
private static void RegularFormat(string fmt, params object[] args)
{
Console.WriteLine(String.Format(fmt, args));
}
private static void SafeFormat(string fmt, params object[] args)
{
string errorString = fmt;
try
{
errorString = String.Format(fmt, args);
}
catch (System.FormatException) { } //logging string arguments were not correct
Console.WriteLine(errorString);
}
}
}
namespace StringExtensions
{
public static class StringExtensionsClass
{
public static string SafeFormat(this string s, string fmt, params object[] args)
{
string formattedString = fmt;
try
{
formattedString = String.Format(fmt, args);
}
catch (System.FormatException) { } //logging string arguments were not correct
return formattedString;
}
}
}
Not sure what I'm doing wrong here. The extension method is not recognized.
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Text.RegularExpressions;
using StringExtensions;
namespace ConsoleApplication1
{
class Program
{
static void Main(string[] args)
{
RunTests();
}
static void RunTests()
{
try
{
///SafeFormat
SafeFormat("Hi There");
SafeFormat("test {0}", "value");
SafeFormat("test missing second value {0} - {1}", "test1");
SafeFormat("{0}");
//regular format
RegularFormat("Hi There");
RegularFormat("test {0}", "value");
RegularFormat("test missing second value {0} - {1}", "test1");
RegularFormat("{0}");
///Fails to recognize the extension method here
string.SafeFormat("Hello");
}
catch (Exception ex)
{
Console.WriteLine(ex.ToString());
}
Console.ReadLine();
}
private static void RegularFormat(string fmt, params object[] args)
{
Console.WriteLine(String.Format(fmt, args));
}
private static void SafeFormat(string fmt, params object[] args)
{
string errorString = fmt;
try
{
errorString = String.Format(fmt, args);
}
catch (System.FormatException) { } //logging string arguments were not correct
Console.WriteLine(errorString);
}
}
}
namespace StringExtensions
{
public static class StringExtensionsClass
{
public static string SafeFormat(this string s, string fmt, params object[] args)
{
string formattedString = fmt;
try
{
formattedString = String.Format(fmt, args);
}
catch (System.FormatException) { } //logging string arguments were not correct
return formattedString;
}
}
}
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评论（4）
您尝试在 type 字符串上调用它。您需要在字符串实例上调用它，例如，
不可否认，这不会执行您想要的操作，因为 SafeFormat 方法实际上完全忽略了第一个参数（
s） 反正。它应该如下所示：然后您可以调用：
扩展方法的要点是它们看起来像扩展类型上的实例方法。您无法在扩展类型上创建看似静态方法的扩展方法。
You're trying to call it on the type string. You need to call it on a string instance, e.g.
Admittedly that won't do what you want it to, because the SafeFormat method is actually completely ignoring the first parameter (
s) anyway. It should look like this:Then you can call:
The point of extension methods is that they look like instance methods on the extended type. You can't create extension methods which appear to be static methods on the extended type.
您正在定义一个实例扩展方法，然后尝试将其用作静态方法。 （C# 无法定义静态扩展方法，尽管 F# 可以定义静态扩展方法。）
而不是：
您想要类似的内容：
即您正在对字符串实例进行操作（在本例中为“Hello”）。
You're defining an instance extension method, and then trying to use it as a static method. (C# is not capable of defining a static extension method, though F# is for that matter.)
Instead of:
you want something like:
i.e. You're operating on the string instance ("Hello" in this case).
扩展方法出现在类型的实例上，而不是类型本身（例如静态成员）。
Extension methods appear on instances of a type, not the type itself (e.g. static members).
尝试
try